Objective:
Objective 1: Identify specific genes associated with Beet necrotic yellow vein virus infection of sugarbeet that contribute to development of rhizomania disease and the ability of the virus to overcome resistance for use as potential targets for induced resistance. This will involve comparisons with other soil-borne pathogens using in-house funds. Completion within 5 years.
Objective 2: Determine environmental and epidemiological factors contributing to the ability of sugarbeet and vegetable viruses to emerge and establish over competing viruses, to provide effective disease management recommendations and prolong the durability of resistance sources.
Specifically:
2.A. Determine the effect of variation among Polymyxa betae isolates on prevalence and dominance of soil-borne viruses affecting sugarbeet, including evaluation of virus competitiveness through collaborative studies involving this project using both in-house funds and those of a local collaborator in NP308. Completion within 5 years.
2.B. Assess accumulation of CYSDV in different host plants in relation to transmission and in development of host resistance using both in-house funds and collaboration with ARS Salinas vegetable breeding program (NP301). Completion within 5 years.
2.C. Identification of factors influencing emergence and dominance of existing and new curtoviruses in North America through analysis of competitive virus accumulation in host plants. Research will involve in-house funds, with completion within 3 years.
Objective 3: Determine environmental and cultural factors contributing to the ability of viruses to induce disease to facilitate breeding efforts for resistance to soil-borne and insect-transmitted viruses affecting lettuce.
Completion of both subobjectives within 5 years using both in-house funds and collaboration with Salinas vegetable project (NP301).
3.A. Develop methods for greenhouse-based evaluation of lettuce for resistance to soilborne tombusviruses through identification of environmental factors influencing disease development, and application of this knowledge to germplasm evaluation using controlled environments.
3.B. Identify sources of tospovirus resistance through evaluation of lettuce and Lactuca germplasm using mechanical transmission and viruliferous thrips under greenhouse conditions, for further development by breeders.
Objective 4: Determine biological and ecological relationships among vectors and their host plants, the pathogens they transmit, and the environment, and develop novel intervention and management strategies for control of vector-borne diseases of vegetables, through the use of traditional, molecular biology, and bioinformatics approaches.

Approach:
Objective 1:
Some defense genes will be common to general sugarbeet or plant defense against pathogens. Determine similarities and differences among pathogens for gene expression between infected and pathogen free host plants based on results of studies currently concluding. Results will be compared with others including BNYVV and other pathogens through parallel studies.
Objective 2:
2.A. Isolates of the plasmodiophorid vector of BNYVV, Polymyxa betae, differ for BNYVV transmission to sugarbeet. This is associated with increased presence of resistance-breaking forms of BNYVV. Single spore isolates of P. betae will be tested for differences in efficiency of BNYVV transmission and effect of vector isolate on virus competitiveness with virus titer.
2.B. Resistance from the exotic melon (Cucumis melo) accession PI 313970 can enhance resistance to CYSDV in cultivated melon, and provide high levels of resistance when combined with resistance source TGR-1551. Exotic melon accessions will be evaluated in replicated field plantings and studies will examine transmission efficiency of CYSDV from resistant and susceptible melons in comparison with virus concentration.
2.C. Individual curtoviruses accumulate to higher or lower titers during single and mixed infections, and this varies by host plant. This influences virus dominance in the field. Curtoviruses will be transmitted by beet leafhoppers from single and mixed infections with qPCR used for virus titer determination. If needed Agro-based delivery of virus isolates to specific hosts, or leafhopper membrane feeding studies could be used for virus delivery.
Objective 3:
3.A. Long-day or high temperature treatment will induce development of tombusvirus symptoms on susceptible lettuce and can be used for selecting resistant and susceptible varieties. Growth chamber experiments will be used to determine optimal environmental conditions (light, temp, soil moisture etc.) for tombusvirus infection of lettuce using mechanical transmission experiments. Chamber and soil moisture and nutrition conditions can be modified as needed.
3.B. Resistance to Impatiens necrotic spot virus (INSV) and Tomato spotted wilt virus (TSWV) exists in wild or cultivated Lactuca germplasm and can be identified through greenhouse evaluation. Transmission of INSV and TSWV to Lactuca germplasm sources will be conducted using thrips vectors in the greenhouse. Virus detection will be performed using standard ELISA. If necessary, virus can be mechanically transmitted directly to lettuce from select hosts.
Objective 4:
Use a combination of bioinformatics analysis of insects with related applied and molecular entomological approaches to examine how insect vectors respond biologically and biochemically to environmental parameters. This will include but is not limited to the responses of whiteflies and leafhoppers to specific host plants, the presence or absence of plant viruses in host plants, and pesticides applied to host plants. Knowledge gained through these studies will be used to develop novel methods for vector population control through both biotechnology-based and genetics approaches.